[Structural Analyses of Toll-like Receptor Sensing Single-stranded Nucleic Acids and Its Application]

Area of Science:

• Immunology
• Structural Biology
• Biochemistry

Background:

• Toll-like receptors (TLRs) are crucial for innate immunity, recognizing microbial components.
• TLR7 and TLR8 specifically recognize single-stranded RNA (ssRNA) and are activated by small-molecule compounds.
• Understanding TLR8 activation mechanisms is key for developing immunomodulatory therapies.

Purpose of the Study:

• To determine the crystal structures of human TLR8 dimers in both unliganded and ligand-activated states.
• To elucidate the structural basis of TLR8 recognition of its natural ligand, ssRNA.
• To investigate how TLR8 distinguishes between different types of ssRNA and chemical ligands.

Main Methods:

• X-ray crystallography was employed to determine the structures of unliganded and ligand-bound human TLR8.
• Crystallographic studies were performed on TLR8 in complex with ssRNA to understand natural ligand recognition.
• Structure-based drug design was utilized to develop novel TLR8 agonists.

Main Results:

• Ligand binding induces a conformational change in the TLR8 dimer, bringing C-termini together for downstream signaling.
• TLR8 recognizes uridine at the dimerization interface, similar to small chemical ligands.
• A distinct, newly identified binding site for short oligonucleotides was discovered on TLR8.
• The crystal structure of a novel TLR8 agonist, C2-butyl furo[2,3-c]quinolone, was determined.

Conclusions:

• Ligand-induced conformational changes in TLR8 dimers are essential for initiating immune responses.
• TLR8 possesses distinct binding pockets for small molecules (like uridine) and ssRNA fragments.
• Structural insights enable the rational design of specific TLR8 agonists for therapeutic applications.